1. Field of the Invention
The present invention relates to a processing method for a substrate, in particular, for conducting, under a condition of reduced pressure, an ashing process or the like upon the substrate, such as for example, a semiconductor wafer or a glass substrate.
2. Description of Prior Art
For the purpose of effectively conducting processing such as an ashing process under a condition of reduced pressure, conventionally, an apparatus is known in which a load-lock chamber is provided in addition to a processing chamber. In the apparatus, while a substrate is processed in the processing chamber, another substrate to be processed next is loaded into the load-lock chamber to wait, and the load-lock chamber is depressurized to the pressure of the processing chamber. After the processing in the processing chamber is completed, the treated substrate in the processing chamber is taken out, and the untreated substrate waiting in the load-lock chamber is transferred into the processing chamber by means of a robot provided in the load-lock chamber.
In the aforementioned processing apparatus, since a general-purpose robot is provided in the load-lock chamber, thereby enabling transfer of substrates from a cassette and transfer of substrates from and to the processing chamber by means of the robot, the robot becomes complex and large-scaled in the structure and the load-lock chamber volume also becomes large. Therefore, time is required for depressurizing the load-lock chamber to the pressure of the processing chamber. Furthermore, a large quantity of power is necessary for depressurizing the load-lock chamber.
The present inventors have already proposed a processing apparatus, for example, in Japanese Patent Application Laid-open No. Hei 10-30183 (1998), in which a transfer robot is provided on the outside of the load-lock chamber, while the inside thereof is provided a handler unit for transferring substrates from the transfer robot and for transferring substrates from and to the processing chamber. Therefore, by making the structure of the handler unit simple, it is possible to obtain a small volume load-lock chamber.
In such a conventional processing apparatus, comprising the aforementioned load-lock chamber, a waiting chamber is provided below the processing chamber for generating plasma. The waiting chamber and the load-lock chamber communicate with each other through a shutter. Accordingly, for processing a substrate, the load-lock chamber, the processing chamber, and the waiting chamber have the same pressure, so as to conduct the following steps: transferring a substrate from the load-lock chamber to the waiting chamber, closing the shutter between the load-lock chamber and the waiting chamber, inserting the substrate from the waiting chamber to the processing chamber while reducing the pressure within the waiting chamber and the processing chamber, and generating plasma within the processing chamber, so as to conduct a predetermined treatment.
As was mentioned above, in a conventional processing method which uses the apparatus comprising the load-lock chamber, the waiting chamber and the processing chamber have the same pressure at the time of conducting an ashing treatment to the substrate in the processing chamber.
The processing chamber is, in many cases, made of synthetic quartz, but in general, the waiting chamber is made of aluminum alloy, having been treated with alumilite on the interior surfaces thereof.
Plasma is easy to generate in lower pressure. Therefore, in a case of the conventional processing method, since the waiting chamber is also in a depressurized condition during processing, residual gas remaining within the waiting chamber in a very small amount sometimes becomes plasma in consequence of the influence of applying high frequency power for generating plasma.
Once plasma is generated within the waiting chamber, plasma generated in the processing chamber becomes unstable due to the change in impedance. There is also a possibility of metal contamination occurring through peeling or flaking of the alumilite thin film due to the plasma, since the waiting chamber is made of aluminum alloy having been treated with alumilite on the interior surfaces thereof.
Therefore, for solving problems such as were mentioned above, the present invention provides a processing method which uses a processing apparatus in which a waiting chamber is provided below a processing chamber and a load-lock chamber is provided in addition to the waiting chamber, wherein pressure within the waiting chamber is kept high enough for no plasma to be generated therein, during which time a substrate is treated within the processing chambers in which plasma is generated under a depressurized condition. The pressure in the waiting chamber is, specifically, preferred to be in a range of 200 Pa to 3000 Pa.
Because generation of plasma in the waiting chamber is controlled during processing of a substrate, plasma is stably generated in the processing chamber without change in impedance of the processing portion as a whole. Also, drawbacks of the waiting chamber can be solved, such as peeling of the alumilite thin film applied to the interior surfaces of the waiting chamber.